as an intercalary form between the
_Semnopitheci_ and the _Macaci_; and among the _Carnivora_, _Hyoenictis_
and _Ictitherium_ as intercalary, or, perhaps, linear types between the
_Viverridoe_ and the _Hyoenidoe_.

Hardly any order of the higher _Mammalia_ stands so apparently separate
and isolated from the rest as that of the _Cetacea_; though a careful
consideration of the structure of the pinnipede _Carnivora_, or Seals,
shows, in them, many an approximation towards the still more completely
marine mammals. The extinct _Zeuglodon_, however, presents us with an
intercalary form between the type of the Seals and that of the Whales.
The skull of this great Eocene sea-monster, in fact, shows by the narrow
and prolonged interorbital region; the extensive union of the parietal
bones in a sagittal suture; the well-developed nasal bones; the distinct
and large incisors implanted in premaxillary bones, which take a full
share in bounding the fore part of the gape; the two-fanged molar teeth
with triangular and serrated crowns, not exceeding five on each side in
each jaw; and the existence of a deciduous dentition--its close relation
with the Seals. While, on the other hand, the produced rostral form of
the snout, the long symphysis, and the low coronary process of the
mandible are approximations to the cetacean form of those parts.

The scapula resembles that of the cetacean _Hyperoodon_, but the supra-
spinous fossa is larger and more seal-like; as is the humerus, which
differs from that of the _Cetacea_ in presenting true articular surfaces
for the free jointing of the bones of the fore-arm. In the apparently
complete absence of hinder limbs, and in the characters of the vertebral
column, the _Zeuglodon_ lies on the cetacean side of the boundary line;
so that upon the whole, the Zeuglodonts, transitional as they are, are
conveniently retained in the cetacean order. And the publication, in
1864, of M. Van Beneden's memoir on the Miocene and Pliocene _Squalodon_,
furnished much better means than anatomists previously possessed of
fitting in another link of the chain which connects the existing
_Cetacea_ with _Zeuglodon_. The teeth are much more numerous, although
the molars exhibit the zeuglodont double fang; the nasal bones are very
short, and the upper surface of the rostrum presents the groove, filled
up during life by the prolongation of the ethmoidal cartilage, which is
so characteristic of the majority of the _Cetacea_